In the fabrication processes for a semiconductor device, numerous processing steps must be carried out on a semiconductor substrate before the device is fabricated. The numerous processes may be as many as several hundred processing steps. Each processing step is executed in a process chamber, such as an etcher, a physical vapor deposition chamber (a.k.a., a sputtering chamber), a chemical vapor deposition chamber, and the like.
In the vast majority of the processing steps, a special environment of either a high vacuum, a low vacuum, a gas plasma or other chemical environment may be provided for the wafer. For instance, in a sputtering chamber, a high vacuum environment may first be provided surrounding the wafer such that metal particles sputtered from a metal target can travel to and deposit on an exposed surface of the wafer. In other process chambers, such as in a plasma enhanced chemical vapor deposition chamber, a plasma cloud of a reactant gas or gases is formed over a wafer positioned in a chamber such that deposition of a chemical substance can occur on the wafer. During any processing step, the wafer must also be kept in an extremely clean environment without the danger of being contaminated. The processing of a wafer therefore must be conducted in a hermetically sealed environment that is completely isolated from the ambient atmosphere.
In a wafer processing system, the handling of wafers between the various chambers must be carefully conducted to avoid damage to the wafers. To accomplish such purpose, the wafer is handled by a wafer transfer system. The wafer transfer system may consist mainly of a robotic handler which handles all wafer transfers by a single, planar, two-axis, random access, cassette-to-cassette motion. A major component of the robotic handler is a wafer blade. The wafer blade may operate under a high-temperature transfer environment of up to 700° Celsius, for example, without incurring contamination.
The positioning of a wafer on the wafer blade may result in two surfaces being positioned face-to-face. When the two surfaces are positioned face to face, the wafer may slip off the wafer blade during transport and the contact between the wafer blade and wafer may cause damage to the wafer and/or the wafer blade. Also, when a wafer falls off the blade, the wafer may be either severely damaged or broken, resulting in a total loss.